Pentene isomerization and etherification

ABSTRACT

An improved process is disclosed for the isomerization of pentenes using a catalyst comprising a non-zeolitic molecular sieve. It is of particular interest to increase the proportion of olefins containing tertiary carbons in the product with low formation of undesirable by-products. Product olefins may be further processed to obtain methyl t-amyl ether, which enjoy high current interest as components for reformulated gasoline. Pentenes in raffinate from etherification may be returned to the isomerization process.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of prior copendingapplication Ser. No. 814,167, filed Dec. 30, 1991, now U.S. Pat. No.5,191,146, which is a continuation-in-part of application Ser. No.670,139, filed Mar. 15, 1991, now U.S. Pat. No. 5,132,484, which is acontinuation-in-part of application Ser. No. 442,879, now abandoned, thecontents of all of which are incorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved process for the conversion ofhydrocarbons, and more specifically for the catalytic isomerization ofolefinic hydrocarbons.

2. General Background

Olefinic hydrocarbons are feedstocks for a variety of commerciallyimportant addition reactions to yield fuels, polymers, oxygenates andother chemical products. The specific olefin isomer, considering theposition of the double bond or the degree of branching of thehydrocarbon, may be important to the efficiency of the chemical reactionor to the properties of the product. The distribution of isomers in amixture of olefinic hydrocarbons is rarely optimum for a specificapplication. It is often desirable to isomerize olefins to increase theoutput of the desired isomer.

Butenes are among the most useful of the olefinic hydrocarbons havingmore than one isomer. A high-octane gasoline component is produced froma mixture of butenes in many petroleum refineries principally byalkylation with isobutane; 2-butenes (cis- and trans-) generally are themost desirable isomers for this application. Secondary-butyl alcohol andmethylethyl ketone, as well as butadiene, are other importantderivatives of 2-butenes. Demand for 1-butene has been growing rapidlybased on its use as a comonomer for linear low-density polyethylene andas a monomer in polybutene production. Isobutene finds application insuch products as methyl methacrylate, polyisobutene and butyl rubber.The most important derivative influencing isobutene demand and buteneisomer requirements, however, is methyl t-butyl ether (MTBE) which isexperiencing rapid growth in demand as a gasoline component.

Pentenes also are valuable olefinic feedstocks for fuel and chemicalproducts. Isoprene, which may be produced by dehydrogenation ofisopentene, is an important monomer in the production of elastomers. Toan increasing extent, pentenes obtained from refinery cracking units arealkylated with isobutane to obtain a high-octane gasoline component. Theprincipal influence on trends in isopentene demand and pentene isomerrequirements, however, is the rapid growth in demand for methyl t-amylether (TAME) as a gasoline component. This derivative is of increasinginterest as restrictions on gasoline olefins and volatility reduce theutility of pentenes as a gasoline component and as ethers and alcoholsare needed for reformulated gasolines with higher oxygen content. Thisinterest may extend to hexenes and higher olefins having tertiarycarbons which could be reacted to yield high-octane ethers.

Olefin isomers rarely are obtained in a refinery or petrochemicalproduct in a ratio matching product demand. In particular, there is awidespread need to increase the proportion of isobutene, isopentane andother tertiarycarbon olefins for production of MTBE, TAME and otherethers. Catalytic isomerization to alter the ratio of isomers is onesolution to this need. Since ethers must be supplied at lower cost tofind widespread use as a fuel product and since isomerization competeswith increased feedstock processing as a source of desired isomers, anisomerization process must be efficient and relatively inexpensive. Inone aspect, a catalytic isomerization process must recognize olefinreactivity: isobutene in particular readily forms oligomers which couldrequire a reconversion step to yield monomer if produced in excess. Theprincipal problem facing workers in the art therefore is to isomerizeolefins to increase the concentration of the desired isomer whileminimizing product losses to heavier or lighter products.

3. Related Art

Processes for the isomerization of olefinic hydrocarbons are widelyknown in the art. Many of these use catalysts comprising phosphate. U.S.Pat. No. 2,537,283 (Schaad), for example, teaches an isomerizationprocess using an ammonium phosphate catalyst and discloses examples ofbutene and pentene isomerization. U.S. Pat. No. 3,211,801 (Holm et al.)discloses a method of preparing a catalyst comprising precipitatedaluminum phosphate within a silica gel network and the use of thiscatalyst in the isomerization of butene-1 to butene-2. U.S. Pat. Nos.3,270,085 and 3,327,014 (Noddings et al.) teach an olefin isomerizationprocess using a chromium-nickel phosphate catalyst, effective forisomerizing 1-butene and higher alpha-olefins. U.S. Pat. No. 3,304,343(Mitsutani) reveals a process for double-bond transfer based on acatalyst of solid phosphoric acid on silica, and demonstrates effectiveresults in isomerizing 1-butene to 2-butenes. U.S. Pat. No. 3,448,164(Holm et al.) teaches skeletal isomerization of olefins to yieldbranched isomers using a catalyst containing aluminum phosphate andtitanium compounds. U.S. Pat. No. 4,593,146 teaches isomerization of analiphatic olefin, preferably 1-butene, with a catalyst consistingessentially of chromium and amorphous aluminum phosphate. None of theabove references disclose the olefin-isomerization process using thenon-zeolitic molecular sieve (NZMS) of the present invention.

The art also contains references to the related use of zeoliticmolecular sieves. U.S. Pat. No. 3,723,564 (Tidwell et al.) teaches theisomerization of 1-butene to 2-butene using a zeolitic molecular sieve.U.S. Pat. No. 3,751,502 (Hayes et al.) discloses the isomerization ofmono-olefins based on a catalyst comprising crystalline aluminosilicatein an alumina carrier with platinum-group and Group IV-A metalliccomponents. U.S. Pat. No. 3,800,003 (Sobel) discloses the employment ofa zeolite catalyst for butene isomerization. U.S. Pat. No. 3,972,832(Butler et al.) teaches the use of a phosphorus-containing zeolite, inwhich the phosphorus has not been substituted for silicon or aluminum inthe framework, for butene conversion. None of the above teach the use ofNZMS for selective butene isomerization, and Butler et al. discloseshigh yields of heavier olefins from butenes at a range of temperatureswith a phosphorus-containing zeolite.

U.S. Pat. No. 4,503,282 (Sikkenga) reveals a process for convertinglinear alkenes to isomerized alkenes using a crystalline borosilicatemolecular sieve, with examples demonstrating the conversion of linearbutenes to isobutene. U.S. Pat. No. 5,132,467 (Haag et al.), filed Mar.6, 1991, teaches a combination of two-stage etherification followed bycommon fractionation and olefin isomerization; the isomerization iscarried out over a medium-pore metallosilicate catalyst with a range ofZSMs and MCM-22 being disclosed. The isomerization of olefins usingNZMS, containing tetrahedral aluminum, phosphorus and at least one otherelement, has not been disclosed in the above references.

U.S. Pat. No. 5,107,050 (Gaffney et al.), filed Dec. 28, 1990, disclosesbutene isomerization using a MgAPSO or SAPO molecular sieve at atemperature above 900° F. U.S. Pat. No. 5,136,108 (Gaffney et al.),filed Mar. 6, 1991, teaches a combination process for producing TAMEand/or TAA by reacting tertiary pentenes with methanol and/or water,distillation to separate reactants, and isomerization of C₅ hydrocarbonswith return of branched hydrocarbons to TAME/TAA production; preferredisomerization catalysts are SAPOs and MgAPSOs.

"Non-zeolitic molecular sieves" or "NZMSs" as referenced herein includethe "SAPO" silicoaluminophosphates of U.S. Pat. No. 4,440,871 (Lok etal.), the "FAPO" ferroaluminophosphates of U.S. Pat. No. 4,554,143(Messina et al.), and the metal aluminophosphates of U.S. Pat. No.4,567,029 (Wilson et al.) wherein the metal is at least one of Mn, Co,Zn and Mg. The application of NZMS-containing catalyst to theisomerization of a C₈ aromatics stream is revealed in U.S. Pat. No.4,740,650 (Pellet et al.). U.S. Pat. No. 4,689,138 teaches a process forisomerizing normal and slightly branched paraffins using a catalystcomprising SAPO molecular sieves. The use of MgAPSO compositions forhydrocarbon conversion is taught in U.S. Pat. No. 4,882,038. However,none of these references discloses or suggests the isomerization ofolefins using a catalyst containing NZMS and having the absence of ahydrogenation promoter.

SUMMARY OF THE INVENTION Objects

It is an object of the present invention to provide an improved processfor the isomerization of olefinic hydrocarbons. A corollary objective ofthe invention is to minimize product losses from an olefin isomerizationprocess.

Summary

This invention is based on the discovery that a catalytic isomerizationprocess using a catalyst comprising at least one NZMS and having theabsence of a platinum-group metal demonstrates surprising efficiency inconverting 2-butene to isobutene or 1-butene in a butene-isomerizationoperation and in the skeletal isomerization of pentenes.

Embodiments

A broad embodiment of the present invention is directed to the catalyticisomerization of olefinic hydrocarbons using a catalyst containing atleast one NZMS and having the absence of a hydrogenation promoter.

In a preferred embodiment, the feedstock to catalytic isomerizationcomprises principally butenes. In a highly preferred embodiment, thecatalytic isomerization increases the concentration of isobutene in theproduct. An alternative preferred embodiment comprises the isomerizationof linear pentenes to isopentene.

In another aspect, the NZMS of the catalyst comprisessilicoaluminophosphates or "SAPO." In an alternative embodiment, thecatalyst comprises a MgAPSO sieve.

These as well as other objects and embodiments will become apparent fromthe detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the approach to equilibrium isobutene concentration in thereactor product, relative to reaction temperature, when employingcatalysts of the invention and of the prior art. The proportion ofisobutene relative to total butenes for each test was divided by theequilibrium proportion of isobutene, calculated from API ResearchProject 44, at the respective reaction temperature of the test.

FIG. 2 shows the yield of heavy (high-boiling) material as a percentageof total product, relative to the reaction temperature of each test, forcatalysts of the invention and of the prior art. This figure thusindicates the loss of isobutene to heavy product in an isomerizationprocess directed to isobutene reproduction.

FIG. 3 shows conversion and selectivity for the isomerization of1-pentene to isopentenes over a period of about 480 hours.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To reiterate, a broad embodiment of the present invention is directed tothe catalytic isomerization of olefinic hydrocarbons using a catalystcontaining at least one NZMS.

Process

According to the process of the present invention, an olefinichydrocarbon charge stock is contacted with a catalyst containing atleast one NZMS in a hydrocarbon isomerization zone. Contacting may beeffected using the catalyst in a fixed-bed system, a moving-bed system,a fluidized-bed system, or in a batch-type operation. In view of thepotential attrition loss of the valuable catalyst and of the operationaladvantages, a fixed-bed system is preferred. The conversion zone may bein one reactor or in separate reactors with suitable means therebetweento ensure that the desired isomerization temperature is maintained atthe entrance to each reactor. The reactants may contact the catalyst inthe liquid phase, a mixed vapor-liquid phase, or a vapor phase.Preferably, the reactants contact the catalyst in the vapor phase. Thecontact may be effected in each reactor in either an upward, downward,or radial-flow manner.

The charge stock may contact the catalyst in the absence of hydrogen orin presence of hydrogen in a molar ratio to charge stock of from about0.01 to about 10. Hydrogen may be supplied totally from outside theisomerization process, or the outside hydrogen may be supplemented byhydrogen separated from reaction products and recycled to the chargestock. Inert diluents such as nitrogen, argon, methane, ethane and thelike may be present. Although the principal isomerization reaction doesnot consume hydrogen, there may be net consumption of hydrogen in suchside reactions as cracking and olefin saturation. In addition, hydrogenmay suppress the formation of carbonaceous compounds on the catalyst andenhance catalyst stability.

In the group of olefinic hydrocarbons suitable as feedstock to thecatalytic isomerization process of the present invention, mono-olefinshaving from 4 to 10 carbon atoms per molecule are preferred. Themono-olefins should be present in the feedstock in a concentration offrom about 0.5 to 100 mass %, and preferably from about 5 to 100 mass %,with most of the balance usually comprising paraffins. Butenes are anespecially preferred feedstock. The feedstock should be rich in one ormore of the linear butenes, i.e., 1-butene, cis-2-butene andtrans-2-butene, if isobutene is the desired product.

An advantageous alternative feedstock within the group of preferredolefins comprises pentenes, often designated amylenes. Optimally one orboth of the linear pentenes 1-pentene and 2-pentene are isomerized toone or more of the isopentenes 2-methyl-2-butene, 2-methyl-1-butene, and3-methyl-1-butene. A pentene-containing feedstock also may containhexenes and, optionally, higher olefins.

The feedstock olefins may be contained in product streams frompetroleum-refining, synthetic-fuel, or petrochemical operations such ascatalytic cracking, thermal cracking, stream pyrolysis, oligomerization,and Fischer-Tropsch synthesis. Often the feedstock contains paraffinssuch as butanes, pentanes, and C₆ and higher paraffins. An advantageousfeedstock for isobutene or isopentene production is raffinate from anetherification process. The derivation of the feedstock from anetherification process is well known and is described, inter alia, in apaper by Bruno Notari, et al., "Skeletal Isomerization of Olefins," atthe 1980 NPRA Annual Meeting in New Orleans on Mar. 23-25, 1980.

These streams may require removal of polar contaminants such as sulfur,nitrogen or oxygen compounds by, e.g., extraction or adsorption tomaintain isomerization-catalyst stability. Raffinate from anetherification process would beneficially be water-washed to removemethanol and other oxygenates present at levels which could affect theperformance of the present catalyst. Removal of dienes and acetylenes,e.g., by selective hydrogenation or polymerization, also may bedesirable.

In an alternative embodiment, from about 10 to 300 mass ppm of anorganic chloride promoter may be added to the charge stock.

Isomerization conditions include reaction temperatures generally in therange of about 50° to 750° C. For the isomerization of butenes toincrease the concentration of isobutene temperatures in the range of200° to 600° C., and especially 250° to 400° C., are preferred.Selective butene isomerization to produce 1-butene is effectedpreferably at temperatures of from 50° to 300° C. Pentene isomerizationis advantageously performed at temperatures in the range of about 200°to 500° C. Reactor operating pressures usually will range from aboutatmospheric to 50 atmospheres. The amount of catalyst in the reactorswill provide an overall weight hourly space velocity of from about 0.5to 100 hr⁻¹, and preferably from about 1 to 40 hr⁻¹.

The particular product-recovery scheme employed is not deemed to becritical to the present invention; any recovery scheme known in the artmay be used. Typically, the reactor effluent will be condensed and thehydrogen and inerts removed therefrom by flash separation. The condensedliquid product then is fractionated to remove light materials from theliquid product. The selected isomer, e.g., isobutene or 1-butene or theisopentene isomer mixture, may be separated from the liquid product byadsorption, fractionation, extraction or reaction. A preferred reactionfor separation of either isobutene or isopentene is etherification forproduction of methyl or ethyl t-butyl ether or for methyl t-amyl ether,respectively. Production of ethers from tertiary olefins is known in theart and described, inter alia, in J. D. Chase, et al., "MTBE and TAME--aGood Octane Boosting Combo," Oil and Gas Journal, Apr. 9, 1979, pp.149-152. The raffinate from the separation step may be returned to theisomerization zone for further conversion to the selected isomer. Thecombination of olefin isomerization and etherification in a processcombination has been widely disclosed, e.g., in a paper by Bruno Notari,et al., "Skeletal Isomerization of Olefins," at the 1980 NPRA AnnualMeeting in New Orleans on Mar. 23-25, 1980, U.S. Pat Nos. 3,979,461(Ancillotti et al.) and 4,554,386 (Groenveld et al.), and FrenchPublication 2 614 297 (Gaillard et al.), incorporated herein byreference for disclosure of the state of the art of theisomerization/etherification combination.

Catalyst

An essential component of the catalyst of the present invention is atleast one non-zeolitic molecular sieve, also characterized as "NZMS" anddefined in the instant invention to include molecular sieves containingframework tetrahedral units (TO₂) of aluminum (AlO₂), phosphorus (PO₂)and at least one additional element (EL) as a framework tetrahedral unit(ELO₂). "NZMS" includes the "SAPO" molecular sieves of U.S. Pat. No.4,440,871, "ELAPSO" molecular sieves as disclosed in U.S. Pat. No.4,793,984 and certain "MeAPO", "FAPO", "TAPO" and "MAPO" molecularsieves, as hereinafter described. Crystalline metal aluminophosphates(MeAPOs where "Me" is at least one of Mg, Mn, Co and Zn) are disclosedin U.S. Pat. No. 4,567,029, crystalline ferroaluminophosphates (FAPOs)are disclosed in U.S. Pat. No. 4,554,143, titanium aluminophosphates(TAPOs) are disclosed in U.S. Pat. No. 4,500,651, MAPO metalaluminophosphates wherein M is As, Be, B, Cr, Ga, Ge, Li or V aredisclosed in U.S. Pat. No. 4,686,093, and binary metal aluminophosphatesare described in Canadian Patent 1,241,943. ELAPSO molecular sieves alsoare disclosed in patents drawn to species thereof, including but notlimited to GaAPSO as disclosed in U.S. Pat. No. 4,735,806, BeAPSO asdisclosed in U.S. Pat. No. 4,737,353, CrAPSO as disclosed in U.S. Pat.No. 4,738,837, CoAPSO as disclosed in U.S. Pat. No. 4,744,970, MgAPSO asdisclosed in U.S. Pat. No. 4,758,419 and MnAPSO as disclosed in U.S.Pat. No. 4,793,833. The aforementioned patents are incorporated hereinby reference thereto. The nomenclature employed herein to refer to themembers of the aforementioned NZMSs is consistent with that employed inthe aforementioned applications or patents. A particular member of aclass is generally referred to as a "-n" species wherein "n" is aninteger, e.g., SAPO-11, MeAPO-11 and ELAPSO-31. In the followingdiscussion on NZMSs set forth hereinafter the mole fraction of the NZMSare defined as compositional values which are plotted in phase diagramsin each of the identified patents, published applications or copendingapplications.

The preferred NZMSs are the silicoaluminophosphate molecular sievesdescribed in U.S. Pat. No. 4,440,871. The silicoaluminophosphatemolecular sieves are disclosed as microporous crystallinesilicoaluminophosphates, having a three-dimensional microporousframework structure of PO₂ ⁺, AlO₂ ⁻ and SiO₂ tetrahedral units, andwhose essential empirical chemical composition on an anhydrous basis is:

    mR:(Si.sub.x Al.sub.y P.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracystalline pore system; "m" represents the moles of "R" presentper mole of (Si_(x) Al_(y) P_(z))O₂ and has a value of from 0.02 to 0.3;"x", "y" and "z" represent, respectively, the mole fractions of silicon,aluminum and phosphorus present in the oxide moiety, said mole fractionsbeing within the compositional area bounded by points A, B, C, D and Eon the ternary diagram which is FIG. 1 of U.S. Pat. No. 4,440,871, andrepresent the following values for "x", "y" and "z":

    ______________________________________                                               Mole Fraction                                                          Point    x              y      z                                              ______________________________________                                        A        0.01           0.47   0.52                                           B        0.94           0.01   0.05                                           C        0.98           0.01   0.01                                           D        0.39           0.60   0.01                                           E        0.01           0.60   0.39                                           ______________________________________                                    

The silicoaluminophosphates of U.S. Pat. No. 4,440,871 are generallyreferred to therein as "SAPO" as a class, or as "SAPO-n" wherein "n" isan integer denoting a particular SAPO such as SAPO-11, SAPO-31, SAPO-40and SAPO-41. The especially preferred species SAPO-11 as referred toherein is a silicoaluminophosphate having a characteristic X-ray powderdiffraction pattern which contains at least the d-spacings set forthbelow:

    ______________________________________                                        SAPO-11                                                                                                      Relative                                       2r                    d        Intensity                                      ______________________________________                                        9.4-9.65              9.41-9.17                                                                              m                                              20.3-20.6             4.37-4.31                                                                              m                                              21.0-21.3             4.23-4.17                                                                              vs                                             21.1-22.35            4.02-3.99                                                                              m                                              22.5-22.9 (doublet)   3.95-3.92                                                                              m                                              23.15-23.35           3.84-3.81                                                                              m-s                                            ______________________________________                                    

Ferroaluminophosphates are disclosed in U.S. Pat. No. 4,554,143,incorporated herein by reference, and have a three-dimensionalmicroporous crystal framework structure of AlO₂, FeO₂, and PO₂tetrahedral units and have an essential empirical chemical composition,on an anhydrous basis, of:

    mR:(Fe.sub.x Al.sub.y P.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracrystalline pore system; "m" represents the moles of "R"present per mole of (Fe_(x) Al_(y) P_(z))O₂ and has a value of from zeroto 0.3, the maximum value in each case depending upon the moleculardimensions of the templating agent and the available void volume of thepore system of the particular ferroaluminophosphate involved; "x", "y",and "z" represent the mole fractions of iron, aluminum and phosphorus,respectively, present as tetrahedral oxides, representing the followingvalues for "x", "y", and "z":

    ______________________________________                                               Mole Fraction                                                          Point    x              y      z                                              ______________________________________                                        A        0.01           0.60   0.39                                           B        0.01           0.39   0.60                                           C        0.35           0.05   0.60                                           D        0.35           0.60   0.05                                           ______________________________________                                    

When synthesized the minimum value of "m" in the formula above is 0.02.The iron of the FeO₂ structural units can be in either the ferric orferrous valence state, depending largely upon the source of the iron inthe synthesis gel. Thus, an FeO₂ tetrahedron in the structure can have anet charge of either -1 or -2. While it is believed that the Fe, Al andP framework constituents are present in tetrahedral coordination withoxygen (and are referred to herein as such), it is theoreticallypossible that some minor fraction of these framework constituents arepresent in coordination with five or six oxygen atoms. It is not,moreover, necessarily the case that all of the Fe, Al and/or P contentof any given synthesized product is a part of the framework in theaforesaid types of coordination with oxygen. Some of each constituentmay be merely occluded or in an yet undetermined form and may or may notbe structurally significant.

For convenience in describing the ferroaluminophosphates, the"shorthand" acronym "FAPO" is sometimes employed hereinafter. Toidentify the various structural species which make up the generic classFAPO, each species is assigned a number and is identified, for example,as FAPO-11, FAPO-31 and so forth.

MeAPO molecular sieves are crystalline microporous aluminophosphates inwhich the substituent metal is one of a mixture of two or more divalentmetals of the group magnesium, manganese, zinc and cobalt and aredisclosed in U.S. Pat. No. 4,567,029. Members of this novel class ofcompositions have a three-dimensional microporous crystal frameworkstructure of MO⁻² 2, AlO⁻ 2 and PO₂ + tetrahedral units and have anessential empirical chemical composition, on an anhydrous basis, of:

    mR:(M.sub.x Al.sub.y P.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracrystalline pore system; "m" represents the moles of "R"present per mole of (M_(x) Al_(y) P_(z))O₂ and has a value of from zeroto 0.3, the maximum value in each case depending upon the moleculardimensions of the templating agent and the available void volume of thepore system of the particular metal aluminophosphate involved; "x", "y",and "z" represent the mole fractions of the metal "M", (i.e., magnesium,manganese, zinc and cobalt), aluminum and phosphorus, respectively,present as tetrahedral oxides, said mole fractions being such that theyare within the following limiting values for "x", "y", and "z":

    ______________________________________                                               Mole Fraction                                                          Point    x              y      z                                              ______________________________________                                        A        0.01           0.60   0.39                                           B        0.01           0.39   0.60                                           C        0.35           0.05   0.60                                           D        0.35           0.60   0.05                                           ______________________________________                                    

When synthesized the minimum value of "m" in the formula above is 0.02.

The CoAPSO molecular sieves of U.S. Pat. No. 4,744,970 havethree-dimensional microporous framework structures of CoO₂ ⁻², AlO₂ ⁻,PO₂ + and SiO₂ tetrahedral units and have an empirical chemicalcomposition on an anhydrous basis expressed by the formula:

    mR: (Co.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracrystalline pore system; "m" represents the molar amount of "R"present per mole of (Co_(w) Al_(x) P_(y) Si_(z))O₂ and has a value offrom zero to about 0.3; and "w", "x", "y" and "z" represent the molefractions of cobalt, aluminum, phosphorus and silicon, respectively,present as tetrahedral oxides, where the mole fractions "w", "x", "y"and "z" are each at least 0.01 and are generally defined, as beingwithin the limiting compositional values or points as follows:

    ______________________________________                                        Mole Fraction                                                                 Point   x             y      (z + w)                                          ______________________________________                                        A       0.60          0.38   0.02                                             B       0.38          0.60   0.02                                             C       0.01          0.60   0.39                                             D       0.01          0.01   0.98                                             E       0.60          0.01   0.39                                             ______________________________________                                    

The MgAPSO molecular sieves of U.S. Pat. No. 4,758,419 have a frameworkstructure of MgO₂ ⁻², AlO₂ ⁻, PO₂ ⁺, and SiO₂ tetrahedral units havingan empirical chemical composition on an anhydrous basis expressed by theformula:

    mR: (Mg.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracrystalline pore system; "m" represents the molar amount of "R"present per mole of (Mg_(w) Al_(x) P_(y) Si_(z))O₂ and has a value ofzero to about 0.3; and "w", "x", "y" and "z" represent the molefractions of elemental magnesium, aluminum, phosphorus and silicon,respectively, present as tetrahedral oxides. The mole fractions "w","x", "y" and "z" are generally defined as being within the limitingcompositional values or points as follows:

    ______________________________________                                        Mole Fraction                                                                 Point   x             y      (z + w)                                          ______________________________________                                        A       0.60          0.38   0.02                                             B       0.39          0.59   0.02                                             C       0.01          0.60   0.39                                             D       0.01          0.01   0.98                                             E       0.60          0.01   0.39                                             ______________________________________                                    

The MnAPSO molecular sieves of U.S. Pat. No. 4,793,833 have a frameworkstructure of MnO₂ ⁻², AlO₂ ⁻, PO₂ ⁺, and SiO₂ tetrahedral units havingan empirical chemical composition on an anhydrous basis expressed by theformula:

    mR: (Mn.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2

wherein "R" represents at least one organic templating agent present inthe intracrystalline pore system; "m" represents the molar amount of "R"present per mole of (Mn_(w) Al_(x) P_(y) Si_(z))O₂ and has a value ofzero to about 0.3; and "w", "x", "y" and "z" represent the molefractions of element manganese, aluminum, phosphorus and silicon,respectively, present as tetrahedral oxides. The mole fractions "w","x", "y" and "z" are generally defined as being within the limitingcompositional values or points as follows:

    ______________________________________                                        Mole Fraction                                                                 Point   x             y      (z + w)                                          ______________________________________                                        A       0.60          0.38   0.02                                             B       0.38          0.60   0.02                                             C       0.01          0.60   0.39                                             D       0.01          0.01   0.98                                             E       0.60          0.01   0.39                                             ______________________________________                                    

It is within the scope of the invention that the catalyst comprises twoor more NZMSs. Preferably the NZMSs are as a multi-compositional,multi-phase composite having contiguous phases, a common crystalframework structure and exhibiting a distinct heterogeneity incomposition, especially wherein one phase comprises a depositionsubstrate upon which another phase is deposited as an outer layer. Suchcomposites are described in U.S. Pat. No. 4,861,739, incorporated hereinby reference thereto. In a highly preferred embodiment the layeredcatalyst comprises a crystalline aluminophosphate of U.S. Pat. No.4,310,440 and a SAPO, especially ALPO-11 and SAPO-11.

The NZMS preferably is combined with a binder for convenient formationof catalyst particles. The binder should be porous, adsorptive supporthaving a surface area of about 25 to about 500 m² /g, uniform incomposition and relatively refractory to the conditions utilized in thehydrocarbon conversion process. By the term "uniform in composition," itis meant that the support be unlayered, have no concentration gradientsof the species inherent to its composition, and be completelyhomogeneous in composition. Thus, if the support is a mixture of two ormore refractory materials, the relative amounts of these materials willbe constant and uniform throughout the entire support. It is intended toinclude within the scope of the present invention carrier materialswhich have traditionally been utilized in hydrocarbon conversioncatalysts such as: (1) refractory inorganic oxides such as alumina,titanium dioxide, zirconium dioxide, chromium oxide, zinc oxide,magnesia, thoria, boria, silica-alumina, silica-magnesia,chromia-alumina, alumina-boria, silica-zirconia, etc.; (2) ceramics,porcelain, bauxite; (3) silica or silica gel, silicon carbide, clays andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated, for example attapulgusclay, diatomaceous earth, fuller's earth, kaolin, kieselguhr, etc.; (4)crystalline zeolitic aluminosilicates, either naturally occurring orsynthetically prepared such as FAU, MEL, MFI, MOR, MTW (IUPAC Commissionon Zeolite Nomenclature), in hydrogen form or in a form which has beenexchanged with metal cations, (5) spinels such as MgAl₂ O₄, FeAl₂ O₄,ZnAl₂ O₄, CaAl₂ O₄, and other like compounds having the formula MOAl₂ O₃where M is a metal having a valence of 2; and (6) combinations ofmaterials from one or more of these groups.

The preferred binder to effect a selective finished catalyst is a formof amorphous silica. The preferred amorphous silica is a synthetic,white, amorphous silica (silicon dioxide) powder which is classed aswet-process, hydrated silica. This type of silica is produced by achemical reaction in a water solution, from which it is precipitated asultra-fine, spherical particles. It is preferred that the BET surfacearea of the silica is in the range from about 120 to 160 m² /g. A lowcontent of sulfate salts is desired, preferably less than 0.3 wt. %. Itis especially preferred that the amorphous silica binder be nonacidic,e.g., that the pH of a 5% water suspension be neutral or basic (pH about7 or above).

NZMS and binder are combined to form an extrudable dough, having thecorrect moisture content to allow for the formation of extrudates withacceptable integrity to withstand direct calcination. Extrudability isdetermined from an analysis of the moisture content of the dough, with amoisture content in the range of from 30 to 50 wt. % being preferred.Extrusion is performed in accordance with the techniques well known inthe art. A multitude of different extrudate shapes are possible,including, but not limited to, cylinders, cloverleaf, dumbbell andsymmetrical and asymmetrical polylobates. It is also within the scope ofthis invention that the extrudates may be further shaped to any desiredform, such as spheres, by any means known to the art.

An optional component of the present catalyst is a platinum-group metalincluding one or more of platinum, palladium, rhodium, ruthenium,osmium, and iridium. Preferably the catalyst is substantially free of ahydrogenation promoter such as a Group VIII (8-10) metal which wouldresult in economically significant losses of olefins to paraffinsthrough hydrogenation. The preferred catalyst contains less than 100mass parts per million (ppm) on an elemental basis of hydrogenationpromoter, and optimally less than about 10 mass ppm. It is especiallypreferred that the catalyst be substantially free of platinum andpalladium.

The catalyst of the present invention may contain a halogen component.The halogen component may be either fluorine, chlorine, bromine oriodine or mixtures thereof. Chlorine is the preferred halogen component.The halogen component is generally present in a combined state with theinorganic-oxide support. The halogen component is preferably welldispersed throughout the catalyst and may comprise from more than 0.2 toabout 15 wt. %, calculated on an elemental basis, of the final catalyst.

The optional halogen component may be incorporated in the catalyst inany suitable manner, either during the preparation of theinorganic-oxide support or before, while or after other catalyticcomponents are incorporated. For example, the carrier material maycontain halogen and thus contribute at least some portion of the halogencontent in the final catalyst. The halogen component or a portionthereof also may be added to the catalyst during the incorporation ofother catalyst components into the support. Also, the halogen componentor a portion thereof may be added to the catalyst by contacting with thehalogen or a compound, solution, suspension or dispersion containing thehalogen before or after other catalyst components are incorporated intothe support. Suitable compounds containing the halogen include acidscontaining the halogen, e.g., hydrochloric acid. The halogen componentor a portion thereof may be incorporated by contacting the catalyst witha compound, solution, suspension or dispersion containing the halogen ina subsequent catalyst regeneration step. The catalyst composite is driedat a temperature of from about 100° to about 320° C. for a period offrom about 2 to about 24 or more hours and calcined at a temperature offrom 400° to about 650° C. in an air atmosphere for a period of fromabout 0.1 to about 10 hours. The optional halogen component may beadjusted by including a halogen or halogen-containing compound in theair atmosphere.

EXAMPLES

The following examples are presented to demonstrate the presentinvention and to illustrate certain specific embodiments thereof. Theseexamples should not be construed to limit the scope of the invention asset forth in the claims. There are many possible other variations, asthose of ordinary skill in the art will recognize, which are within thespirit of the invention.

EXAMPLE I

Example I illustrates the conversion of a feedstock rich in 2-butenesover a catalyst of the invention with reaction temperature as theprincipal variable. The composition of the feedstock was as follows inmass %:

    ______________________________________                                        Butanes           0.497                                                       Isobutene         0.538                                                       2-butenes         94.747                                                      Heavy components  4.217                                                       ______________________________________                                    

Product yields are expressed as mass % of the total products. Theapproach to equilibrium butene-isomer distribution was determined byreference to equilibrium values calculated from free energies offormation contained in "Selected Values of Physical and ThermodynamicProperties of Hydrocarbons and Related Compounds," API Research Project44 (1953). This approach to equilibrium is expressed for isomerizationto isobutene in FIG. 1 as % of isobutene equilibrium relative toreaction temperature.

Catalysts were evaluated using a 1/2-inch stainless-steel tube as amicro-reactor. One gram of catalyst as powder was placed in the reactor.Butene-rich feedstock was charged to the reactor at its vapor pressureat 70° F. by a syringe pump. The reaction temperature was monitored by athermocouple in the catalyst bed and controlled by heating the reactorin a fluidized sandbath. Sandbath temperature was controlled by athermocouple. The liquid products were analyzed by vapor-phasechromatography.

Catalyst performance was compared using a Figure of Merit, or FOM. FOMis obtained by multiplying the mass percent of desired product(isobutene or 1-butene) in the total reactor products by the ratio of(desired product)/(desired product plus light plus heavy byproducts).The first term is a measure of conversion as well as selectivity, whilethe second term reflects selectivity. Thus, FOM is a measure ofconversion and selectivity with an emphasis on selectivity. FOM isreported hereinbelow at the reactor temperature at which it reaches itsmaximum value for each of the catalysts.

The process of the present invention was demonstrated by effectingisomerization of 2-butene to isobutene over SAPO-11 catalyst. SAPO-11catalyst is characterized as described hereinabove, and the specificcatalyst samples used in these tests had the following approximateproperties:

    ______________________________________                                        Composition, mass %:                                                                             Al.sub.2 O.sub.3                                                                      41.7                                                                  P.sub.2 O.sub.5                                                                       50.5                                                                  SiO.sub.2                                                                              7.8                                                                          100.0                                              ______________________________________                                    

The 2-butene-rich feedstock described above was charged to themicro-reactor, operating at atmospheric pressure. Reaction temperaturewas increased in a series of steps, and two or more product analyseswere performed at each temperature. The results shown below representaverage results at each temperature:

    ______________________________________                                        Temperature, °C.                                                                     260°                                                                          318°                                                                             343°                                                                        370°                               WHSV          2.2    1.5       4.7  5.2                                       Products, mass %                                                              C.sub.3 and lighter                                                                         0.1    1.0       2.7  2.2                                       Butanes       2.5    2.8       3.5  2.8                                       Isobutene     9.6    13.2      26.7 23.4                                      1-butene      15.8   13.2      11.8 11.1                                      2-butenes     66.0   53.8      38.1 37.8                                      C.sub.5 and heavier                                                                         6.0    16.0      17.2 22.7                                      ______________________________________                                    

EXAMPLE II

A control of the prior art was developed to contrast with the process ofthe present invention. A zeolitic molecular-sieve catalyst was testedfor the isomerization of 2-butene to isobutene. The catalyst had thefollowing approximate characteristics:

    ______________________________________                                        Composition, mass %:                                                                             Al.sub.2 O.sub.3                                                                      4.3                                                                   SiO.sub.2                                                                             95.6                                                                  CaO      0.1                                                                          100.0                                              ______________________________________                                    

Tests were performed and results measured using the feedstock andprocedures of Example I. Results were as follows:

    ______________________________________                                        Temperature, °C.                                                                    261°  290°                                                                          317°                                  WHSV         2.9          5.0    4.1                                          Products, mass %:                                                             C.sub.3 and lighter                                                                        1.0          3.6    1.0                                          Butanes      0.9          2.0    0.5                                          Isobutene    1.1          3.0    1.2                                          1-butene     14.2         4.7    1.9                                          2-butenes    74.5         16.5   7.4                                          C.sub.5 and heavier                                                                        8.3          70.2   88.0                                         ______________________________________                                    

Temperatures were not increased above 320° C., as the proportion ofisomerization became irrelevant due to the increasing predominance ofthe reaction forming heavy components.

EXAMPLE III

The test results used to develop Examples I and II were compared withequilibrium isomer values based on the aforementioned API ResearchProject 44, and the results were plotted in FIG. 1. Data based onindividual tests are shown in FIG. 1, whereas the tables of Examples Iand II are based on averages of test results at substantially equivalenttemperatures.

The process based on the catalyst of the invention achieves asubstantially higher conversion to isobutene than the catalyst of theprior art. The equilibrium data understate the advantage of the presentinvention; due to the high yield of heavy product when using theprior-art catalyst.

FIG. 2 shows the yield of heavy (high boiling) material relative toreaction temperature for processes using the catalysts of both thepresent invention and the prior art. At temperatures of 290° C. andabove, where isomerization to isobutene becomes significant, the presentinvention avoids the predominant reaction to heavy product of the priorart.

The comparative maximum FOM and corresponding temperatures were asfollows, with two data points presented to show a range of operatingtemperatures:

    ______________________________________                                                  SAPO-11 (Invention)                                                                        Zeolite (Prior Art)                                    ______________________________________                                        FOM         15.5     17.6      0.2    0.3                                     Temperature °C.                                                                    288°                                                                            344°                                                                             261°                                                                          291°                             ______________________________________                                    

EXAMPLE IV

The process of the present invention was demonstrated using FAPO-11 andFAPO-31 catalysts for 1-butene production from 2-butene. FAPO catalystsare described earlier in this specification, and the specific catalystsamples used in these tests had the following approximate properties:

    ______________________________________                                                           FAPO-11                                                                              FAPO-31                                             ______________________________________                                        Composition, mass %:                                                                          Al.sub.2 O.sub.3                                                                       37.3     39.7                                                        P.sub.2 O.sub.5                                                                        57.1     50.1                                                        Fe.sub.2 O.sub.3                                                                        5.6     10.2                                                                 100.0    100.0                                       ______________________________________                                    

Tests were performed using the feedstock and procedures of Example I,with the exception that conversion to 1-butene with minimum isobuteneby-product was achieved at lower temperatures. Results were as follows:

    ______________________________________                                                  FAPO-11     FAPO-31                                                 ______________________________________                                        Temperature, °C.                                                                   148°                                                                          203°                                                                           260°                                                                        149°                                                                         205°                                                                        260°                        WHSV 3.1    3.6    2.9     4.1  2.7   4.4                                     Products, mass %                                                              C.sub.3 and lighter                                                                       0.0    0.0     0.0  0.0   0.0  0.0                                Butanes     0.5    0.5     0.5  0.6   0.5  0.6                                Isobutene   0.0    0.0     1.5  0.0   0.0  0.2                                1-butene    1.9    10.0    17.3 4.8   13.8 17.4                               2-butene    94.1   86.4    75.9 90.1  79.0 73.6                               C.sub.5 and heavier                                                                       3.5    3.1     4.8  4.5   6.7  8.2                                ______________________________________                                    

The yield of 1-butene at reaction temperatures of above 200° is aboveequilibrium-concentration values. By-product isobutene varies from nilto less than 10% of 1-butene within the ranges shown.

The maximum FOM and corresponding temperatures were as follows, using1-butene yield as the criterion and designating difficult-to-separateisobutene as a byproduct:

    ______________________________________                                                       FAPO-11                                                                              FAPO-31                                                 ______________________________________                                        FOM              13.0     12.7                                                Temperature, °C.                                                                        260°                                                                            261°                                         ______________________________________                                    

EXAMPLE V

Isomerization of 1-pentene to isopentene, as a combination of 2-methylpentene-1 and 2-methyl pentene-2, was demonstrated over SAPO-11catalyst. The SAPO-11 catalyst of Example I was extruded with a silicabinder and used for pilot-plant testing of pentene conversion andproduct selectivity. The feedstock was a mixture of 1-pentene andisopentane containing about 38 mass % pentene. Hydrogen was present at amolar ratio to 1-pentene of about 8. Reactor pressure was about 18atmospheres, and temperature was varied between 327° and 357° C. After a50-hour line-out period, pentene conversion averaged about 70% and molaryields from converted pentene were as follows:

    ______________________________________                                        C.sub.3 and lighter                                                                            0.3                                                          Butenes/butanes  1.8                                                          Isopentenes      93.4                                                         C.sub.6 and heavier                                                                            4.6                                                          ______________________________________                                    

The pilot-plant run was maintained over a period of about 480 hours inorder to establish catalyst stability. The results of the extended runare plotted in FIG. 3.

EXAMPLE VI

Further pilot-plant tests were performed on the Example V feedstockmixture of 1-pentene and isopentane, using the same bound SAPO-11catalyst, in order to assess the effect of operating temperature onconversion and selectivity. Operating pressure was about 10 atmospheres,and temperatures assessed were 327° and 427° C. Pentene conversion andmolar yields from converted pentene were as follows:

    ______________________________________                                        Temperature, °C.                                                                          427°                                                                          327°                                         Conversion, %      68.7   64.4                                                Selectivity, mol %                                                            C.sub.3 and lighter                                                                              2.2    0.2                                                 Butenes/butanes    2.2    0.8                                                 Isopentenes        91.5   94.6                                                C.sub.6 and heavier                                                                              3.3    2.1                                                 ______________________________________                                    

We claim:
 1. A process for the isomerization of pentenes which comprisescontacting a pentene-containing feedstock, comprising raffinate pentenesfrom an etherification process, at isomerization conditions with acatalyst containing at least one non-zeolitic molecular sieve to providea product containing at least one pentene isomer in greaterconcentration than in the feedstock.
 2. The process of claim 1 whereinthe pentene isomer comprises one or more of the isopentenes.
 3. Theprocess of claim 1 wherein the isomerization is carried out in thepresence of free hydrogen.
 4. The process of claim 1 wherein theisomerization conditions comprise a temperature of from about 200° to600° C., a pressure of from about atmospheric to 50 atmospheres, and aweight hourly space velocity of from about 0.5 to 100 hr⁻¹.
 5. Theprocess of claim 1 wherein the non-zeolitic molecular sieve is selectedfrom the group consisting of SAPOs, FAPOs, CoAPSOs, MnAPSOs, MgAPSOs andmixtures thereof.
 6. The process of claim 5 wherein the non-zeoliticmolecular sieve is selected from the group consisting of SAPO-11,SAPO-31 and SAPO-41.
 7. The process of claim 6 wherein the non-zeoliticmolecular sieve is SAPO-11.
 8. The process of claim 1 wherein thecatalyst comprises an inorganic oxide matrix component.
 9. The processof claim 8 wherein the inorganic oxide matrix comprises silica.
 10. Theprocess of claim 1 wherein the catalyst comprises a halogen component.11. A process for the skeletal isomerization of pentenes which comprisescontacting a feedstock, comprising raffinate pentenes from anetherification process, at isomerization conditions with a catalystcontaining at least one non-zeolitic molecular sieve to provide aproduct containing a greater concentration of one or more of theisopentenes than in the feedstock.
 12. The process of claim 11 whereinthe isomerization is carried out in the presence of free hydrogen. 13.The process of claim 11 wherein the isomerization conditions comprise atemperature of from about 200° to 600° C., a pressure of from aboutatmospheric to 50 atmospheres, and a weight hourly space velocity offrom about 0.5 to 100 hr⁻¹.
 14. The process of claim 11 wherein thenon-zeolitic molecular sieve is selected from the group consisting ofSAPOs, FAPOs, CoAPSOs, MnAPSOs, MgAPSOs and mixtures thereof.
 15. Theprocess of claim 14 wherein the non-zeolitic molecular sieve is selectedfrom the group consisting of SAPO-11, SAPO-31 and SAPO-41.
 16. Theprocess of claim 15 wherein the catalyst contains less than 100 mass ppmof a hydrogenation promoter.
 17. The process of claim 11 wherein thecatalyst comprises an inorganic oxide matrix component.
 18. The processof claim 17 wherein the inorganic oxide matrix comprises silica.